1. Field of the Invention
The present invention relates generally to an apparatus and method for improving diagnoses. Particularly, the present invention relates to an apparatus and method for altering the intravenous delivery of pharmaceuticals to improve therapy and diagnosis. Even more particularly, the present invention relates to an apparatus and method for altering the intravenous delivery of pharmaceuticals to improve therapy and diagnosis using contrast agents that enhance nuclear magnetic resonance signals.
2. Description of the Related Art
Arterial diseases and injuries are common and sometimes have severe consequences including death. Imaging arteries serves to screen, detect and characterize arterial disease before these consequences occur. It also serves to define anatomic features that may provide assistance when planning surgery or vascular intervention.
In the practice of clinical medicine, numerous pharmaceutical products are administered intravenously. Some of these pharmaceuticals are used for diagnostic purposes and include contrast agents such as iodinated contrast-media used in x-ray angiography (XRA) and Computed Tomography Angiography (CTA), gadolinium chelates used in Magnetic Resonance Angiography (MRA) and radioactive agents used in nuclear medicine such as 99m-Tc-labeled Sestamibi or 201-Thallium. Some pharmaceuticals are administered intravenously for therapeutic purposes, for example, I-131 Sodium Iodide for thyroid cancer and perhaps in the future, pharmaceuticals for gene-therapy. All of these intravenously administered agents have in common the fact that they are distributed throughout the body by way of the blood stream.
One of the advantages of the x-ray techniques is that image data can be acquired at a high rate so that a sequence of images may be acquired during injection of the contrast agent. Such dynamic studies enable one to select the image in which the bolus of contrast agent is flowing through the vasculature of interest. Images showing circulation of blood in the arteries and veins of the kidneys, the neck and head, the extremities and other organs have immense diagnostic utility. Unfortunately, these x-ray methods subject the patient to potentially harmful ionization radiation and often require the use of an invasive catheter to inject a contrast agent into the vasculature to be imaged.
MRA uses the nuclear magnetic resonance (NMR) phenomenon to produce images of the human vasculature. When a substance such as human tissue is subjected to a uniform magnetic field, the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field. A signal is emitted by the excited spins, and after the excitation signal is terminated, this signal may be received and processed to form an image. When utilizing these signals to produce images, magnetic field gradients are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well-known reconstruction techniques.
To enhance the diagnostic capability of MRA, a contrast agent such as gadolinium can be injected into the patient prior to the MRA scan. Excellent diagnostic images may be acquired using contrast-enhanced MRA if the data acquisition is properly timed with the bolus passage. The non-invasiveness of MRA makes it a valuable screening tool for cardiovascular diseases. Screening typically requires imaging vessels in a large volume. This is particularly true for diseases in the runoff vessels of the lower extremity.
In MRA, contrast material injected into a vein in the upper extremity travels by vein to the right atrium of the heart. From there it travels to the right ventricle, then to the lungs where it is oxygenated. It returns to the left atrium of the heart, then to the left ventricle, the aorta, the common iliac artery, the internal and external iliac, the common femoral, and then throughout the smaller arteries of the thigh and leg. As the arterial blood passes through the lower extremities, it enters the capillaries of the muscles and then returns to the heart via the venous system. MRA of the lower extremities is done to visualize the vascular structures to determine the extent that some of the arteries (or veins) of the leg may be narrowed or partially blocked. Effective images can be made only while there is contrast material in the blood vessel being imaged. There exists only a short window of opportunity, approximately 30 to 45 seconds, when the contrast material is in the iliac, femoral and lower leg arteries when these images can be obtained and before the contrast material has entered the venous phase.
U.S. Pat. No. 5,928,148 (1999, Wang et al.) discloses a method of performing magnetic resonance angiography over a large field of view using table stepping. The MRA data is acquired from a large region of interest by translating the patient to successive stations at which successive portions of the MRA data set are acquired. Patient movement is chosen to track a bolus of contrast agent as it passes through the region of interest to achieve maximum image contrast. In one embodiment, a stationary local coil is supported adjacent the patient to acquire the MRA data. In another embodiment, a multi-segment local coil moves with the patient and its segments are sequentially switched into operation.
U.S. Pat. No. 5,924,987 (1999, Meaney et al.) discloses a method and apparatus for magnetic resonance arteriography using contrast agents. Meaney et al. disclose a technique of and a system for imaging vascular anatomy over a distance considerably greater than the maximum practical field of view of a magnetic resonance imaging system while using substantially one contrast agent injection. A plurality of image volumes are acquired that are representative of different portion""s of the patient""s body.
U.S. Pat. No. 5,553,619 (1996, Prince) discloses a method and apparatus for administration of contrast agents for use in magnetic resonance arteriography. The method and apparatus adapts the timing of a maximum or substantially elevated rate of infusion to correlate with the collection of image data corresponding to the center of k-space. Adapting the timing of a maximum or substantially elevated rate of infusion to correlate with the collection of image data corresponding to the center of k-space provides a period of a maximum or substantially elevated contrast concentration in the artery of interest relative to adjacent veins during collection of at least a portion of the image data corresponding to the center of k-space.
U.S. Pat. No. 5,417,213 (1995, Prince) discloses a method of imaging arteries distinctly from veins using nuclear magnetic resonance imaging in combination with intravenous administration of a magnetic resonance contrast agent. The contrast agent is injected in such a way that the arterial contrast concentration is substantially higher than the venous and background tissue concentration for a sufficiently long period of time to acquire the magnetic resonance image. The injection site of the contrast agent is chosen such that it is in a vein that is remote from the artery of interest.
U.S. Pat. No. 6,037,771 (2000, Liu et al.) discloses a sliding thin-slab method of acquiring three-dimensional MRA data. Liu et al. discloses the use of a 3DFT gradient-recalled echo pulse sequence to acquire NMR data from which an MR angiogram is produced. A thin slab excitation is employed and this thin slab is incremented in slice-thickness steps through the volume of interest as the NMR data is acquired. Navigator echoes are acquired at each thin slab location to correct the NMR data for phase errors produced by the sliding slab technique.
A disadvantage presented by the prior art is that the amount of imaging time required to make high-quality images is long compared to the amount of time the contrast material is in the arterial circulation. Effective images can be made only while there is contrast material in the blood vessel being imaged. The imaging time window is approximately 30 to 45 seconds after the contrast material enters the particular region to be imaged. Waiting too long before beginning the imaging shortens the already tight xe2x80x9cwindow of opportunityxe2x80x9d the technologist has to obtain the desired number of images. Imaging beyond the xe2x80x9cwindow of opportunityxe2x80x9d produces images of lesser and even poor quality with regard to the purpose for imaging the vasculature in the first place. This is so because the contrast material may have already passed through the arteries of the leg and into the veins. Imaging the veins provides the radiologist with no information about the state of the arteries, i.e. blockage of the arteries.
Another disadvantage of the prior art is directly related to the imaging xe2x80x9cwindow of opportunity.xe2x80x9d Resolution in magnetic resonance imaging is a function of time. The longer the bolus of contrast material is in the arteries being imaged, the better the quality of the pictures.
Therefore, what is needed is an apparatus and method for extending the xe2x80x9cwindow of opportunityxe2x80x9d for imaging arteries containing a contrast agent. What is further needed is an apparatus and method for extending optimal imaging time by keeping the blood containing the contrast agent longer in the arteries undergoing imaging.
It is an object of the present invention to provide an apparatus and method for extending the imaging time when imaging arteries containing a contrast agent. It is another object of the present invention to provide an apparatus and method for extending optimal imaging time by keeping the blood containing the contrast agent longer in the arteries undergoing imaging. It is a further object of the present invention to provide an apparatus and method to regulate blood flow and, thus, affect the distribution of pharmaceuticals both proximal and distal to the site where the pressure is applied. It is yet another object of the present invention to provide an apparatus and method that alters the intravenous delivery of pharmaceuticals to improve therapy and diagnosis.
The present invention achieves these and other objectives by providing a device and method for raising the pressure in the veins of an extremity in order to slow the arterial blood flow. Imaging the lower extremities is done to visualize the arterial structures to determine the extent that some of the arteries of the leg may be narrowed and partially blocked. Effective images can be made only while there is contrast material in the blood vessel being imaged. Thus, there is only a short window of opportunity, approximately 30 to 45 seconds, when the contrast material is in the iliac, femoral and lower leg arteries to make the images. If an operator waits too long or does not have enough time to get the desired number of images, the blood containing the contrast material may have already passed through the arteries of the leg and into the veins.
Raising the pressure in the veins of an extremity in order to slow arterial blood flow allows the contrast agent to remain in the extremity longer providing higher resolution images. Because image resolution is a function of time, the longer the contrast material is in the arteries of the extremity, the better is the quality of the images that can be obtained. When the pressure applied to an extremity exceeds venous pressure, venous return of blood to the heart is slowed. When the pressure applied to an extremity exceeds diastolic pressure, arterial blood flow is slowed. When the applied pressure exceeds arterial systolic pressure, all blood flow is stopped. Varying degrees of pressure affect blood flow and thus affect the distribution and concentration of any intravenously administered chemical substance. The application of pressure to an extremity concomitant with the intravenous administration of a pharmaceutical can alter the amount of an agent that is delivered to that extremity. Furthermore, because altering the blood flow to an extremity can also alter the cardiac output, applying pressure to an extremity can modulate the delivery of an intravenous agent to other areas of the body as well.
The present invention applies pressure to one or more extremities to alter blood flow. For example, in imaging the lower extremities, external pressure is applied before, during, or after arrival of the pharmaceutical to the leg. If pressure is applied before the pharmaceutical arrives, the filling of the arteries with pharmaceutical is delayed and the transit time of the pharmaceutical is prolonged. The timing of the applied pressure relative to the circulation of the pharmaceutical may be optimized to image certain portions of the lower extremity vasculature (e.g. proximal arteries vs. distal arteries, arteries vs. veins, etc.). This technique may be used to enhance imaging of the vasculature using Magnetic Resonance Angiography (MRA), Computed Tomography Angiography (CTA), or X-ray Angiography (XRA).
By impeding arterial blood flow the present invention allows contrast material to remain visually active longer and at selected levels within the vasculature of the extremity. This achieves more signal and less noise thereby enhancing image resolution. The present invention uses one or more inflatable pressure cuffs to obtain better images during MRA (Magnetic Resonance Angiography) and CTA (Computed Tomography Angiography) by increasing the pressure in one or more extremities of the patient undergoing imaging. When inflated, the inflatable pressure cuffs affect blood flow and, thus, the concentration, duration of action and effectiveness of a contrast agent.
The present invention includes one or more inflatable cuffs connected to a cuff controller unit. The cuff controller unit is controlled and activated by a system controller. The system controller is programmed by an operator. Communication between the system controller and the cuff controller unit occurs by way of an interface. Interface coupling may be accomplished in any number of ways. Examples of such interface coupling are the use of cabling through the penetration panel, the use of electromagnetic control (e.g. infrared) through a window, or the use of optical fiber through a wave-guide.
The inflatable cuffs may be incorporated into an extremity peripheral vascular radio frequency (rf) coil array. The rf coil array and cuffs may be components of a structured table system. The cuffs may be further incorporated into an extremity holding system coupled to the table system. The extremity holding system may be a pivoting, arcuate component that is positioned around the extremity. The arcuate component may be multiple pieces with each piece adapted to incorporate a cuff, or the arcuate component may be a single, extremity-long device having a plurality of predetermined locations adapted to incorporate a cuff in each predetermined location. The pivoting arcuate component of the extremity holding system may also be a two-piece, jaw-like component where each jaw-like component is adapted to pivot towards its other mating component into a closed position to encircle a portion of the extremity and to pivot away from each other into an open position to allow placement or removal of an extremity. The rf coil array and cuffs may also be configured together into a stocking-like or pant-like garment structure that clothes the patient""s extremity undergoing the imaging. The rf coils may be paired to provide upper and lower halves of the rf coils. Alternate geometries of rf coils are also possible such as a series of volumetric coils with each element including both extremities.
For use with existing MRA systems, a pressure-cuff system is employed that includes one or more pressure-inducing bands or cuffs and a pressure-inducing controller unit. The one or more pressure-inducing bands or cuffs may be individually placed about the extremity of an animal, and more particularly a human being, or they may be incorporated into a stocking-like or pant-like garment made of a flexible material. Preferably the garment has a releasable seam that allows the extremity to be easily enclosed/encircled by wrapping the garment structure about the extremity. Each one or more pressure-inducing bands or cuffs is coupled to the controller unit, which in turn is controlled by an operator or by a computer program or both. Each pressure-inducing band or cuff is individually controlled to provide the required pressure in the extremity for enhancing the MRA images.